It was shown that in the yeast Saccharomyces cerevisiae meiosis and sporulation can be initiated not only by nitrogen deprivation but also by partial carbon or phosphate limitation. This is possible only under conditions under which the intracellular concentration can be controlled by the concentration of a compound in the medium. Meiosis and sporulation can also be initiated by the addition of certain inhibitors of nucleotide synthesis and the partial purine deprivation of purine requiring mutants.